1. Field of the Invention
The present invention relates to a turbo-charged compression ignition engine of low compression ratio type.
2. Description of the Prior Art
It is well known that combustion pressure, and hence, output power of an engine are increased as supercharging pressure is increased so that the maximum power output of the engine is determined by the maximum allowable pressure.
It is possible to increase the power, while maintaining the maximum combustion pressure below the maximum allowable pressure, by decreasing the compression ratio. This, however, leads to problems such as difficulty in starting the engine, misfire during light-load operation and so forth. In the case of a diesel engine which is designed to operate at a compression ratio of around 8:1, it is possible to obtain a mean effective pressure of about 32 Kg/cm.sup.2. In the misfire region shown hatched in FIG. 1 of the accompanying drawings, however, the level of the load imposed on the engine is low so that the turbo-charger cannot exert its power. As a result, the pressure and temperature of the induced air are lowered so that the desired ignition temperature is not reached in the compression stroke. In such a case, white or blue smoke having an offensive smell is discharged from the exhaust side of the engine and the engine finally becomes inoperative due to misfiring.
In order to obviate this problem, two countermeasures have been proposed: namely, a variable compression type method and a hyperber method. These countermeasures are, however, used only in weapons because the former requires a complicated control mechanism while the latter suffers from an impractically large drop in thermal efficiency.